'da' is only part of the correct calculus notation here. What are you differentiating with respect to?

The following may help. R is the radius of the circumcircle.

Sine rule.

so, for example:

Bob

]]>http://www.mathisfunforum.com/profile.php?id=676942013-01-07T08:14:17Zhttp://www.mathisfunforum.com/viewtopic.php?pid=247878#p247878If the Sides and Opposites angles of are varing such a way that Circum-Radius Remain Constant.